It is becoming increasingly common to find broadband wireless networking capabilities (e.g., IEEE 802.11, 802.16e, LTE, etc.) in mobile devices. In many network environments, a network device establishes communication with an access point, e.g., a base station of a cellular network, for both uplink and downlink access. OFDMA-based wireless broadband technologies include 3GPP LTE and 3GPP UMB. Mobile WiMAX, for example, uses a scalable orthogonal frequency division multiple access (OFDMA) scheme to deliver wireless broadband packet data services to mobile terminals.
LTE specifications define indicators that reflect the channel state information (CSI) as observed by the receiver of the communication, for example, user equipment, UE. The main indicators include the channel quality indicator (CQI), the rank indication (RI), and the precoding matrix indicator (PMI). The reporting of these indicators is performed either periodically or aperiodically in conjunction with physical uplink control channel (PUCCH) or physical uplink shared channel (PUSCH). Additionally, for multiple-input-multiple-output (MIMO) operation, the selection of either closed-loop or open-loop mode depends on the rate of change in the channel conditions.
In general, the feedback is measured using cell specific reference signal (CRS) which is referred to herein as reference signal (RS). For the first and the second antenna ports, there are eight reference signals per resource block (RB), for the third and fourth antenna ports, there are four reference signals per resource block. Typically, the CQI and PMI are calculated using mean instantaneous capacity (MIC) over the entire RS and thus incur large computation overhead. For example, a wideband CQI calculation over 20 MHz channel may require 16×100 logarithmic operations.